(5х - 10х/х+1) поделить на 15х - 15/4х+4 / - дробь;

5х - 10х/х+1 * 4х+4/15х - 15

-5x/x+1 * 4(x+1)/15x - 15 сокращаем

-20х/15x - 15 = -20x/15(x-1) = -4x/3(x-1)

(5х-10/х+1):(15х-15/4х+4)=5(х-2)*4*(х+1)/(х+1)*15*(х-1)=4(х-2)/3(х-1)=(4х-8)/(3х-3).